The present invention, in some embodiments thereof, relates to a hub gear and, more particularly, but not exclusively, to a multi-speed hub gear where the transmission ratio is changed by engaging one planetary gear set while disengaging another planetary gear set rotating in conjunction.
A conventional speed-changing transmission hub uses a planetary gear train comprising ring gears, rotating gears and central gears. Torque is inputted to the planetary gear train either via the ring gear or the carrier of the rotating gears, as controlled by a clutch, which engages either with the ring gear or with the carrier, thus controlling the path of torque within the planetary gear train and the degrees of freedom of the sun gears for various speeds.